1. Field of the Invention
The present invention relates to a coordinate calculating apparatus and a coordinate calculating program. More particularly, the present invention relates to a coordinate calculating apparatus and a coordinate calculating program for calculating coordinates by capturing predetermined markers using image capturing means.
2. Description of the Background Art
Patent Document 1 (Japanese Patent Laid-Open Publication No. 8-335136) discloses a pointing device comprising image capturing means. This pointing device is used so as to designate an arbitrary position on a display screen. The pointing device detects two markers in an image captured by the image capturing means, and calculates positions of the markers in the image. Thereafter, a position on the display screen which is designated by the pointing device (designated position) is calculated from the positions of the markers. Patent Document 1 also describes that, when makers having two colors (red and green) are used, the colors of the markers are not displayed on the display screen (paragraph 0029), and when the two markers are not detected in a captured image, an error process is performed (paragraph 0042).
In the pointing device of Patent Document 1, when the two markers are not correctly detected, i.e., an image of at least one of the marker is no longer captured, an error process is performed. In other words, only when the two markers are included in the captured image, the pointing device can be operated. Therefore, when one of the markers is not detected, the pointing device cannot be operated even if the other marker is detected. Therefore, the possibility that the pointing device cannot be operated is high.
In addition, a range in which the user can move the pointing device is limited to a range in which images of the two markers are captured, so that the pointing device can be moved only in a narrow range, likely leading to the difficulty for the user to use. Particularly, when a distance between the two markers is large or when a distance between the pointing device and the markers is close, an image of at least one of the markers is located close to an edge of the captured image. In this case, by moving the pointing device by only a short distance, one of the markers disappears from the captured image, so that an error process is performed.